1. Field of the Invention
The present invention relates to an engine cylinder block and, more particularly, to the structure of a lower block section of a cylinder block of an automotive vehicle engine.
2. Description of Related Art
Typically, bearings are installed in engine cylinder blocks to support an engine crankshaft for rotation. If a bearing cap, holding an engine crankshaft for rotation in the engine cylinder block, slants, i.e., inclines with respect to the engine cylinder block during engine operation, the engine crankshaft will rub against the bearing cap and produce vibration. In order to avoid vibration of the engine crankshaft due to slanting of the bearing cap, various bearing cap structures have been proposed by which the structural rigidities of bearing caps are increased.
Each bearing cap in some engine cylinder blocks is bolted by side bolts to a skirt portion of the engine cylinder block. Such a bearing cap fixing structure is described in, for instance, Japanese Unexamined Patent Publication No. 59-88,241. It is also known to fix a bearing cap to both side walls and a bottom wall of a lower block of the engine cylinder block by bolts. Such a bearing cap fixing structure is known from, for instance, Japanese Unexamined Patent Publication No. 1-280,667.
Conventional bearing cap fixing structures have been designed without considering differences in vibration among the bearing caps. Consequently, although a conventional bearing cap fixing structure can improve the static supporting stiffness of a bearing cap, the conventional fixing structure is not always effective to suppress vibrations of the bearing cap while the engine vibrates. When the engine itself and a transmission structurally connected to the engine produce vibrations, the upper cylinder block, the lower cylinder block and the transmission are affected by the vibrations differently, and the upper and lower cylinder blocks partially deform in different ways. For instance, the upper and lower cylinder blocks may deform in different directions. If a bearing cap is fastened to both the upper and lower cylinder blocks in a location at which the upper and lower cylinder blocks deform differently, the bearing cap may possibly slant, cause the crankshaft to bend, and produce vibrations due to such bending.